The present invention concerns a process for the production of a strip of zirconium alloy for nuclear use `Zircaloy 2` (specification ASTM B 52, grades R 60802 and R 60812) or `Zircaloy 4` (same specification, grades R 60804 and R 60814), resulting in the strip being in a `restored` state corresponding to a compromise in respect of mechanical strength and ductility. The term `restored` state is used herein to designate a heat-treated state without complete recrystallisation as in a tempered state in which the stresses due to a cold working operation are at least partly relieved. The present invention also concerns the strip produced.
For the purpose of producing spacer grids which are used in nuclear fuel elements, there is a wish to use strip material of Zircaloy 2 or 4, of a thickness which is typically between 0.3 and 0.9 mm, enjoying both a good elastic limit at the temperature of use and good ductility at ambient temperature (20.degree. C.) as indicated by the uniform elongation in the long direction and also in the transverse direction of the strip, so as to provide a good level of performance in regard to the shaping operations involved in the production of grids. The `uniform elongation` (elongation is referred to herein by A %) is the maximum elongation of a testpiece in a tensile test, before the onset of a contraction in cross-section.
The characteristics which are thus required in respect of the strip are typically as follows:
E.sub.0.2 at 315.degree. C..gtoreq.250 MPa
Uniform A % in the long direction.gtoreq.4 and if possible.gtoreq.5
Uniform A % in the transverse direction.gtoreq.4 and if possible.gtoreq.5.
More precisely, the attempt has been made to produce a strip having the above-indicated characteristics by applying thereto, after rolling, a final heat treatment of short duration, for example in the moving mode, either in the air or in a protective atmosphere, possibly followed by a surface treatment.